Rotifer resting egg densities in lakes of different trophic state, and their assessment using emergence and egg counts

Abstract

The methods for estimating rotifer resting egg densities from lake sediment, and the use of emergence for determining community composition from lakes, were investigated in Lakes Tikitapu and Okaro, New Zealand. Significantly lower (P<0.01) estimates of resting egg densities were obtained by monitoring emergence from incubated sediments than from egg counts. However, incubation of sediments did not require the ability to recognise species on the basis of egg morphology as did egg counts. Significantly higher (P<0.01) densities of resting eggs were found in sediments from eutrophic Lake Okaro than from oligo-mesotrophic Lake Tikitapu. Incubation of sediments did not result in the emergence of all species found in the plankton during an earlier thirteen-month seasonal survey, including some common species. This currently limits the use of this method as a tool for rapid assessment of community composition. However, the method is likely to provide advantages over some traditional methods, such as vertical net hauls, by providing more complete species lists if only a single visit to a site is possible.